Prayers to John McCain and his family/friends. Same situation as Ted Kennedy.
Glial cells, the brain’s immune system.
Not an area of cancer cell formation that we do well with.
As a species we’ve done quite poorly in learning how to deal with those cells when they become problematic.
Until the late 1990’s, in physiology, medicine, exercise physiology, and sport we behaved as if the brain and nervous system didn’t exist.

Muscle, heart, lungs, and blood was everything.
But the brain and nervous system control everything.
.
Now in physiology, medicine, exercise physiology, and sport things are just now getting fully geared up.
Way late for folks that are way down the line with anything from brain degenerative disease [Alzheimer’s, Parkinsons, ALS, schizophrenia, etc] to brain cancer [glioblastoma, etc].
We got caught with our collective pants down.